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Logan Sapphire SI.jpg
The 423-carat (85 g) blue Logan Sapphire
CategoryOxide mineral
(repeating unit)
Aluminium oxide, Al2O3
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (32/m)
Space groupR3c
ColorTypically blue, but varies
Crystal habitAs crystals, massive and granular
FractureConchoidal, splintery
Mohs scale hardness9.0
Specific gravity4.0~4.1
Optical propertiesAbbe number 72.2
Refractive indexnω=1.768–1.772
Birefringence 0.008
Melting point2,030–2,050 °C
Other characteristicsCoefficient of thermal expansion (5.0–6.6)×10−6/K
relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic)[1]

Sapphire is a precious gemstone and a variety of the mineral corundum (α-Al2O3), It is usually blue, but natural "fancy" sapphires also occur in all other colors other than red as red colored corundum is called ruby.[2] The variety in color is due to small amounts of elements such as iron, titanium, chromium, copper, or magnesium mixed in.


  1. Harman, Alang Kasim; Ninomiya, Susumu; Adachi, Sadao (1994). "Optical constants of sapphire (alpha-Al2O3) single crystals". Journal of Applied Physics 76 (12): 8032–8036. Bibcode 1994JAP....76.8032H. doi:10.1063/1.357922.
  2. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).

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